Process for control and regulation of double piston-driven engine with hydrostatic motion transducers

ABSTRACT

A system for controlling the relative positions of the two pistons in double or opposed piston engines having hydrostatic motion transducers for transmitting the piston energy to a driveshaft. The control is effected by adding fluid to or withdrawing fluid from the transducers. The system includes means for comparing the positions of the two pistons and the angle of rotation of the driveshaft to generate two synchronous error signals, and means for comparing the actual dead points of said two pistons and the predetermined nominal dead points of each piston to generate first and second dead point error signals, and for relating the first dead point error signal to the second dead point error signal. Fluid is added to or withdrawn from the hydrostatic motion transducers in accordance with the synchronous error signals when the engine speed is below a selected engine speed, and in accordance with a dead point error signal when said engine speed exceeds a predetermined speed. In the system, control of both pistons is simultaneously switched from the synchronous error signal to the dead point error signal and vice versa.

United States Patent Rabiger [451' Nov. 7, 1972 [54] PROCESS FOR CONTROL AND REGULATION OF DOUBLE PISTON- DRIVEN ENGINE WITH HYDROSTATIC MOTION TRANSDUCERS [72] Inventor: Wolfgang Rabiger, Buckenhofen,

Germany [73] Assignee: Grundig E.M.V., Kurgartenstrasse,

Germany [22] Filed: Dec. 14, 1970 [21] Appl. No.: 97,786

[30] Foreign Application Priority Data Dec. 23, 1969 Germany ..P 19 64 455.4

[52] US. Cl ..60/19, 60/DIG.1, 60/DIG.2 [51] Int. Cl ..F02b 41/00 [58] Field of Search ..60/19, DIG.1, DlG.2

[56] References Cited UNITED STATES PATENTS 3,525,215 8/1970 Conrad ..60/19 3,583,508 6/ 1971 Waddington ..60/19 X 2,588,742 3/1952 McCallum ..60/DIG.2

Primary Examiner-Edgar W. Geoghegan Attorney-Lewis l-l. Eslinger, Alvin Sinderbrand and Curtis, Morris & Safford [5 7] ABSTRACT A system for controlling the relative positions of the two pistons in double or opposed piston engines having hydrostatic motion transducers for transmitting the piston energy to a driveshaft. The control is effected by adding fluid to or withdrawing fluid from the transducer s. The system includes means for comparing the positions of the two pistons and the angle of rotation of the driveshaft to generate two synchronous error signals, and means for comparing the actual dead points of said two pistons and the predetermined nominal dead points of each piston to generate first and second dead point error signals, and for relating the first dead point error signal to the second dead point error signal. Fluid is added to or withdrawn from the hydrostatic motion transducers in accordance with the synchronous error signals when the engine speed is below a selected engine speed, and in accordance with a dead point error signal when said engine speed exceeds a predetermined speed. in the system, control of both pistons is simultaneously switched from the synchronous error signal to the dead point error signal and vice versa. I

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/ Zww 41205 l PROCESS FOR CONTROL AND REGULATION OF DOUBLE PISTON-DRIVEN ENGINE WITH HYDROSTATIC MOTION TRANSDUCERS The invention relates to a method and a system for controlling relative piston position in an opposed piston engine wherein each cylinder has a pair of opposed pistons enclosing a combustion chamber, and wherein the pistons are connected to a driveshaft by hydrostatic motion transducers.

It is known to replace thevconnecting rods and the crankshaft of a piston driven engine with hydrostatic motion transducers which transmit piston movement to the drive shaft of the engine. Many advantages flow from the use of hydrostatic motion transducers in piston driven engines. For example, the engine is very compact by eliminating the connecting rods and Y crankshaft of a typical engine. Further, the piston travel path from bottom to top dead center does not need to exceed one-half of. a revolution of the driveshaft. Still .further, the use of hydrostatic motion transducers may permit the driveshaft to turn more slowly than the piston stroke. In addition, hydrostatic motion transducers avoid the transmission of radial forces from the piston to the driveshaft.

However, the most significant advantage of hydrostatic motion transducers is that it is possible to build very compact opposed piston engines in which each cylinder has a top and a bottom piston symmetrically operable against each other about a common ignition or compression combustion chamber. Construction of opposed piston engines such as for a ship, with conventional mechanical transducers is impractical because of the need for projecting connecting rods between the top pistons and the crankshaft.

A relativelycomplex control system is required when the pistons are connected to the driveshaft by hydrostatic motion transducers each of which include a hydraulic fluid column. The complex control system is necessitated by each hydraulic fluid column being subject to change in length independently of one another as a result of positive or negative leakage to 'each column, and independent changes in temperature and operating pressures. Therefore, the length of each hydraulic fluid column must be controlled when required by the addition or withdrawal of hydraulic fluid from thecolumn.

It has been proposed, in my copending U.S. Patent application Ser. No. 97,787 filed on even date herewith and assigned to a common assignee, to control hydraulic fluid column lengths in a piston engine by generating a synchronous error signal for each piston in response to a comparison of piston position at any given instant with the particular angle of rotation of the driveshaft, and controlling the length of each hydraulic fluid column in response to its respective synchronous error signal below a predetermined engine speed (rpm). The proposal also provides for generating dead center error signals for each piston by comparing respective actual top dead center positions with predetermined top dead center positions, and controlling the length of each hydraulic fluid column in response to respective dead center error signals at or above the predetermined engine speed. Thus, the proposal provides for controlling the position of each piston independently of the others, and has proven highly effective for engines having only one piston within each cylinder.

However, the column control scheme of my copending application is preferably adapted as herein described for use with opposed piston engines. The present invention is necessary because the hydrostatic motion transducers of each piston in a cylinder acts in conjunction to transmit energy from each of the pistons to the driveshaft. Thus, an indication of an error in the length of one hydraulic fluid column may also erroneously call for a change in the other hydraulic fluid column.

In accordance with the present invention, there is provided a method and a system for controlling the relative positions of pistons in an opposed piston engine which includes at least one cylinder having first and second opposed pistons therein to form a combustion chamber between the two pistons. The engine also comprises means including first and second hydrostatic motion transducers connected to the first and the second pistons, respectively, for transmitting piston energy to a driveshaft.

The method of the present invention comprises comparing the positions of the first and the second pistons and the angle of rotation of the driveshaft to respectively generate first and second synchronous error signals for the first and the second pistons. Further, the actual dead center positions of the first and the second pistons are compared with predetermined first and second dead center positions, respectively, to generate first and second dead center error signals, and the first dead center error signal is modified by combining it with a function of the second dead center error signal to generate a modified first dead center error signal. The amount of fluid in each of the first and the second hydrostatic motion transducers is respectively controlled in response to either the first andthe second synchronous error signals or the modified first'dead center error signals and the second dead center error signal.

In accordance with a specific aspect of the invention, the first and the second dead center error signals are combined by subtracting the two signals, for example, by inverting the second dead center error signal and adding it to the first dead center error signal to generate the modified first dead center error signal.

The system of the present invention for controlling the relative positions of pistons in an opposed piston engine comprises means for comparing the positions of the first and the second pistons and the angle of rotation of the driveshaft to generate first and second synchronous error signals for each of the first and the second pistons, and means for comparing the actual dead center positions of the first and the second pistons and predetermined first and second dead center positions, respectively, to generate first and second dead center error signals. The system also includes means for combining a function of the second dead center error signal with the first dead center error signal to generate a modified first dead center error signal. Means are also provided for respectively controlling the amount of fluid in the first and the second hydrostatic motion transducers in response to either the first and the second synchronous error signals or the modified first dead center error signal and the second dead center error signal.

In accordance with a specific wpect of the present invention, the combining means comprises means for Subtracting the second dead center error signal from the first dead center error signal, for example by inverting the second dead center error signal, and adding the inverted second .dead center error signal to the first dead center error signal to generate the modified first dead center error signal.

Thus, the present invention provides for control of the hydraulic fluid columns in an opposed piston engine by simultaneously switching between synchronous and dead center control of the opposed pistons within each cylinder, and also provides for control of one of the opposed pistons within each cylinder in response to its dead center error signalas modified by the dead center signal of the other piston.

The-construction of illustrative embodiments as well as further objects and advantages thereof, will become apparent when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic representation of a cylinder in an opposed piston engine having hydrostatic motion transducers totransmit piston energy to the driveshaft.

FIG. 2 is a block diagram of a:system suitable for control of hydrostaticmotion transducers in an engine having only one piston within each cylinder.

F IG. 3 is a block diagram of a system in accordance with the present invention for controlling the hydrostatic motion transducers in an opposed piston engine.

FIG. 4a is a schematic representation ofan embodiment for generating top dead point error signals in accordance with the present invention.

FIGS. 4b and 4c are representative curves of voltages generated in the circuit of F IG, 4a.

FIG. 5 is another block diagram in accordance with an embodiment of the present invention for controlling hydraulic fluid length in response to synchronous and dead point error signals.

FIG. 6 is a schematic diagram-of an integrator circuit in accordance with an embodiment of the present invention. I

FIG. 7 is a block diagram of another embodiment of the present invention.

FIG. 1 is a diagrammatic representation of a cylinder and hydrostatic motion convertor of an opposed piston engine. With reference to FIG. 1,.a bottom and a top piston 1, 2 enclose a combustion chamber 3 which may be either a spark or a compression ignition chamber. The pistons 1, 2y are aligned such that combustion within the chamber 3 drives the pistons l, 2 apart. The bottom piston 1 is connected by a connecting rod 4 to a piston head of a hydrostatic motion transducer or convertor which comprises a cylinder having a column 9 of hydraulic fluid therein.

The top piston 2 is connected by connecting rods 5, to a pair of piston heads 7, of a hydrostatic motion transducer or convertor comprising two columns of hydraulic fluid 8 positioned on opposite sides of the fluid column 9 which is axially aligned with the pistons l, 2. The effective cross-sectional areaof each one of the piston heads 7 is one half that of the piston head 6.

Combustion'inthe chamber 3 acts to drive the bottom piston l downwardly to directly transmit a force through the connecting rod 4 and the piston head 6 to the center column 9 of hydraulic fluid. Simultaneously, combustion in the chamber 3 drives .the top piston 2 upwardly, vwhich, in turn, acts through the connecting rods 5 to drive the pair of piston heads 7 upwardly, and thus apply a force through the columns of hydraulic .fluid 8 to the top side of the center piston head 6. The

force applied to the top of the center piston head 6 thereby is added to the force directly applied to the center piston head 6 by the bottom piston 1. Thus, the center piston head 6 applies a resultant force of the opposing pistons 1, 2 downwardly through the center column 9 of hydraulic fluid to a rotational transducer or rotational convertor 10 which acts to turn a driveshaft ll.

, The center column 9 of hydraulic fluid is in fluid communication with a control slide 12 by a conduit and the outer columns of hydraulic fluid 8, are in fluid communication with another slide control valve -16. The valve 12 acts in response to a signal 13 applied thereto to add fluid to the column 9 from a pressurized source of hydraulic fluid 14; or to remove hydraulic fluid from the column 9 by connecting column 9 fluid to an ex-- haust 15. Similarly the valve 16 operates under the control of a signal 17. to add hydraulic fluid to column 8 from the pressurized source of hydraulic fluid 14, or to release fluid from column 8 to an exhaust l5; and thereby control the length of the-outer columns of hydraulic fluid 8.1

It is clear from FIG. 1 that the position of the top piston 2 depends upon the height of the outer hydraulic fluid columns 8, and upon the position of the bottom piston l which in turn is dependent upon the height vof the center hydraulic fluid column 9. Thus, an error in height of the center hydraulic fluid column 9 affects both the bottom and the top pistons 1, 2. For example,

if the height of the center column of hydraulic fluid 9 is below a predetermined level, the center piston head 6 falls below a predetermined level and a signal 13 is applied to the valve 12 to add fluid from the pressurized source of hydraulic fluid l4 and thereby add fluid to the center column 9. However, when there is too little fluid in the center column 9, which thereby drops the piston l and the center piston head 6 below their predetermined positions, the outer columns of hydraulic fluid 8 which effectively actaboutthe curved upper endscauses the outer piston heads 7. to rise and thus movethe top piston 2 above its predetermined position. This is due to the fact that as the length of column 9 decreases, the length of the column of fluid above piston 6 in the chamber in which the; piston rides increases. This additional fluid is supplied from the fluid in the columns 8 above pistons 7. As a result, the columns of liquid above pistons 7 are decreased, so that combustion within-chamber 3 will cause pistons 7 to rise above their normal positions. (since they are now resisted by shorter columns of liquid 8), thereby causing piston 2 to also move above its normal predetermined position. When the top piston 2 is above its predetermined position, a control signal 17 is applied to the valve 16 to add more fluid to the outer columns 8 from pressurized source of hydraulic fluid 14. Thus, the control signal 17 may cause an addition of more hydraulic fluid to the outer columns 8 when none is needed.

Similar compounded errors may occur if the center I column 9 is controlled in response to a synchronous error signal while the outer columns 8 are controlled in response to a top dead center or dead point error signal, or vice versa.

FIG. 2 is a block diagram of system .for controlling the amount of fluid in a hydrostatic motion transducer of an engine having only one piston within each cylinder. With reference to FIG. 2, a piston position transmitter 18 applies a signal representative of piston position throughout its stroke to a comparator 20. An angle of crankshaft rotation transmitter 19 also applies a signal representative of crankshaft angle to the comparator 20. The transmitters 18, 19 may be AC function generators and the comparator 20 may be a phase synchronous rectifier which applies a synchronous error signal to an electronic selector switch 25. V

A top dead center transmitter 21 generates an output signal during a very short time interval of the piston stroke when the stroke is in the immediate vicinity of top dead center to a comparator 23, and to an actual dead center error signal generator 22. With reference to FIG. 4, it may be noted that the dead center error signal transmitter 21 and the dead center error signal transmitter 22 can be constructed in a single unit. It is apparent that the time between two dead center signals generated by the transmitter 21 is a measure of engine rotational speed, rpm. A timer 24 which maybe a reference oscillator also applies a signal to the comparator 23. When the time interval between top dead center signals generated by the transmitter 21 decreases to a predetermined value indicative of a predetermined engine speed, the comparator 23 applies a signal to the actual top dead center error signal generator 22 to generate an output which is applied to the switch 25. The comparator 23 simultaneously applies a signal to the switch 25 to cause the switch 25 to pass the actual top dead center error signal 25 to a slide control valve 26 and thus control the amount of fluid in a hydraulic column in response to the dead center error signal. I

Conversely, when the time interval between top dead center signals from the transmitter 21 are at or greater than the predetermined value and thus indicating engine speed below the predetermined value, the comparator 23 causes the switch 25 to pass the v synchronous error signal from the comparator 20 to the valve 26, and thus control the length of the hydraulic column in response to the synchronous error signal.

FIG. 3 is a block diagram of anembodiment of the present invention. With reference to FIG. 3, numerals which are the same as those shown in FIGS. 1 and 2 identify the same components described with reference to FIGS. 1 and 2, and reference numerals having an 0 following them identify components for-controlling the hydrostatic motion transducer of the top piston, and those having a u identify components for controlling the hydrostatic motion transducer of the bottom piston. Piston position transmitters 180, 18a apply signals representative of piston positions for the top and bottom pistons, respectively, to comparators 20o, 20u. The comparators 200, 2014 also receive signals from a crankshaft angle of rotation transmitter 19, and generate output signals to switches 250, 25a, respectively, which are representative of synchronous error. A top dead center signal transmitter 210 generates a signal representative of the actual top dead center position to a mixing circuit 27. Another top dead center position transmitter 2lu also applies a signal representative of the actual dead center position of the bottom piston to the mixing circuit 27. In the mixing circuit 27,

the two signals applied thereto are suitably combined tov apply a modified signal for the top piston position to a top dead center error signal generator 220. The output from the bottom top dead center position transmitter 2lu is also applied to a top dead center error signal generator 22a, and to the comparator 23 of the timing circuit which includes a timer 24. The output from each of the top' dead center error signal generators 220, 22a are applied to the switches 250, 25a, respectively. The switches 250, 25a are actuable by the output from the comparator 23 to pass "either the synchronous error signals from the comparators 200, 20a, or: the top dead center error signals from the generators-22o, 22a as control signals 17, 13 to the valves 16, 12 dependent upon engine speed as discussed hereinabove with reference to FIG. 2.

A circuit for carrying out the function of the top dead center transmitters 210, 2lu is shown in FIG. 4a. The dead center transmitters 21 can generate both the actual dead center signals and by defining a predetermined nominal dead center position generatea real (or referenced) dead center signal. With reference to FIG. 4a, a core 28 of weak magnetic material is connected by a rod (not shown) to the piston being controlled. The core 28 is movable within a coil 29 which comprises a primary winding 31 connected to a source of constant AC voltage 30, and'a pair of first secondary windings 33, 32. The pair of first secondary windings 33, 32 are connected as a differential transformer to a circuit comprising a pair of opposing diodes 62, 63, a pair of capacitors 64, 65, and a pair of resistors 66,67. The core 28 is positioned with respect to the coil 29 such that it begins to enter the coil 29 just before the piston under control reaches a nominal predetermined dead center position. Movement of the core 28 into the coil 29 induces voltages in the secondary windings 33, 32 which are rectified across the capacitors 64, 65 respectively. The development of the voltages across the capacitors 64, 65 as the core 28 insertion depth increases is shown in FIG. 4b as curves I.) and U respectively. The sum of the voltages developed across the capacitors 64, 65 taken between points 68 and 69 is shown in FIG. 40 as the curve identified as U, U The coil 28 has a length identified as L which corresponds to the axial length, L, of the .coil29. The coil 29 is positioned with respect to the core 28 such that the core 28 will be fully inserted in the coil 29 at the predetermined nominal top dead center position such that the voltage developed between points 68, 69 will be zero as identified by A on the U U curve of FIG. 4c.

Another secondary coil 34 is also provided to generate an output voltage across the terminals identified as Up, as the core insertion depth of the core 28 increases. After suitable rectification (not shown) the induced voltage in the secondary winding 34 is shown in FIG. 4c as a function of core insertion depth as curve U The U voltage is used in a more specific embodiment of FIG. 5 to control the storage of a signal representative of the top dead center error signal, i.e.,

the value of U U With reference to FIG. 5,,

reference numerals corresponding to those in earlier figures identify the same components as used in those figures, and 0 refers to elements for controlling the top piston, and u indicates components for controlling the bottom piston. The dead center signal generator 21a for the bottom piston generates output signals as switch 36a and to a threshold impulse transmitter 35a.

If and only if the U, voltage reaches a certain value, e.g., at X in FIG. 40, each of the transmitters 35 generate the leading edge of an impulse, the trailing edge of which will occur when the U voltage decreases beyond another certain value, e.g., at Y in FIG. 40. In order to avoid hunting of the system the leading edge of the impulse is'builtup at a higher threshold level, i.e., in a closer proximity of the piston to the nominal dead point than the trailing edge. As the piston moves so closely to the upper dead point that the threshold level of the device 35 is reached, the leading edge of the im pulse. activates the electronic switch 36 connecting so the voltage U U, to the peak storage device 37. This consists e.g., of a capacitor which is charged to 'a suitable value by the leading edge of the impulse from 35, and therefore, discharged under. the influence of U U, as long as the core 28 moves into the spool 29. When the movement of the piston reverses, so that the core 28 is withdrawn again, then the chargeremaining on the capacitor corresponds-to the actual dead point error; this charge is briefly gated by a gate device into the final signal measuring and storage device 39, the gating being effected by a very short pulse derived from the trailing edge of the impulse from 35 and formedin thepulse shaper 38. The output of the trigger 38u has a short'durationof a few milliseconds. At this time, the peak voltage accumulator 37a is reset for the next measurement. Further, the measured value stored in the accumulator 39a corresponds to the last measured actual top dead center value and also represents the top dead center signal for. the bottom piston as a result of the predetermined top dead center position being defined by the passage of the curve U u, through zero volts of FIG. 4c.

The componentsof the circuit forcontrolling the top piston, specifically the dead center signal generator 210, a transmitter 350, an electronic switch 360, a peak accumulator 370, a trigger 380 and an accumulator 390 of FIG; 5 operate inthe same manner as that described hereinabove with reference to similarly numbered components for the control of the bottom piston.

As discussed hereinabove, the position of the top piston depends upon the state of its hydrostatic motion transducer and also upon the state of the hydrostatic motion transducer -of the bottom piston. Thus, the present invention provides for modifying the 'dead center error signal of the top piston by function of the dead center error signal of the bottom piston to compensate for corrections made to the hydrostatic motion transducer of the bottom piston. The modification of the dead center error signal for the top piston is accomplished in a mixing circuit 27 which is fed by the outputs of the top and bottom accumulators 390, 39a. The mixing circuit-27 is suitably a subtraction circuit which subtracts the dead center error signal for the bottom piston from the dead center error signal for the top piston. Subtraction may be accomplished in the mixing circuit 27 by inverting thedead center error signal from the bottom accumulator 39u, and then aiding the inverted dead center error signal to the dead center error signal ,of the top accumulator 390 to provide a modified dead center error signal for the top piston.

Thedead center error signal stored in the accumulators 390, 3914 may be processed in accordance with a particular engine requirement. For example, the circuit of FIG. 5 provides for applying the signal stored in the bottom accumulator 39u to an amplifier 40a to generate a signal having a magnitude proportional to the error signal applied thereto. The proportional error signal output of the amplifier 40a is applied to an integrator 41a and to the input of an adder circuit 42u. Integration occurs in the integrator circuit 4114 over a predetermined period of time. This predetermined period of time is fixed by an integration impulse former circuit 43a which is actuable by the rear edge of the pulse generated by the impulse former 38a.

The output signal from the transmitter 3514 is also applied to the comparator 23 to measure the time period between successive pulses and thus provide a representation of engine rotational speed. When the engine reaches the predetermined switch-over speed, the comparator 23 provides an output signal tothe switch 25a to remove control of the length of the hydraulic column from the synchronous error signal output of the comparator 20a. The output of the comparator 23 is also applied to the integrator 41a to initiate integration of the proportionalsignal output from the amplifier 4014 over a period as determined by the length of the pulse generated by the impulse former 43a. The integrated output signal from the integrator 41a is applied to the adder 42 wherein it is combined with the proportional output signal fromthe amplifier 40a. The combined signal output from the adder 42a is appliedthrough the switch 2514 as a control signal 13 to control the valve 12 of the hydrostatic motion transducer of the bottom piston.

The modified dead center error signal of the output of the mixing circuit 27 is acted upon by an integration impulse former 430, and integrator circuit 410, an amplifier 400, and an adder 420 in the same manner as described with corresponding components of the control circuit for the bottom piston.

The comparator 23 simultaneously applies an output signal indicative of the engine attaining .the predetermined rotational speed to the integrator41u and the switch 25a of the circuit for the bottom piston and to the integrator 410 and the switch 250 of the circuit for the top piston. Thus, a function of the modified dead center error signal is applied to the valve 16 for controlling the amount of fluid in the hydrostatic motion transducer of the top piston through the switch 250 at the same time that the output from the adder 42a of the bottom circuit is applied to the bottom valve 12.

Thus, the switching between synchronous and dead center control of the hydrostatic motion transducers of the top and bottom pistons occur simultaneously as a result of the timing circuit comprising the timer 24, and the comparator 23 simultaneously switching the electronicswitches 250, 25a and activating or deactivating the integrators 410, 41a. v

The compression of the cylinder may be changed in accordance with the present invention by superimposing a DC voltage upon the dead center error signal voltage of the bottom piston U U, to thus efi'ectively displace passage through the zero voltage point A (FIG.

4c) to the left or right. In accordance with the invention, such modification of the dead center error signal occurs only in the control circuit of the bottom piston and may, for example, be incorporated in the accumulator circuit 39a, but in any case is applied to the bottom dead center error signal U U ata point prior to applying the bottom dead center error signal to the mixing circuit 27.

In another embodiment of the invention, the integrators 41o, 41u may be incorporated in a fail-safe circuit such as that shown in FIG. 6. With reference to FIG. 6,

1. In a system for controlling the relative positions of pistons in an opposed piston engine; wherein said engine' includes at least one cylinder, first and second opposite pistons forming a combustion chamber '"therebetween within said-cylinder, a driveshaft, and

means including first and second hydrostatic motion transducers connected to said first and second pistons, respectively, for transmitting piston energy to said driveshaft; the combination comprising;

the amplifier 40 applies its output signal through a resistor 40 to the input of a capacitor feedback amplifier 44 which is connected in parallel with a capacitor 45 and a field effect transistor 46 and also in parallel with another field effect transistor 48. The amplifier 44 applies its output signal to the adder 42 which was described hereinabove with reference to FIG. 5. When the system is functioning properly, a predetermined voltage 47 is applied to the base of the transistor 46 to turn it on. At this time, the capacitor45 is charged to a value representative of the output of the amplifier 40 and thus is indicative of the position of the valve in the hydrostatic motion transducer under control. However,

should power fail, the predetermined voltage 47 is removed from the transistor 46 to turn the transistor 46 off and thereby retain the last value stored on thecapacitor 45. Since the hydraulic valves controlling the amount of fluid in the hydrostatic motion transducers of the top and bottom pistons will also not change their position as a result of current failure, control operation of the amount of fluid in the two transducers will therefore be begun without surge upon restoration of power because the charge on the capacitor 45 corresponds to its respective valve position. The remaining transistor 48 of FIG. 6 circuit is connected at its base to the output of the comparator 23 of the timing circuit. When the comparator 23 applies a signal to the base 48, the circuit is turned on and integration of the output of the amplifier 40 begins. -1

FIG. 7 shows another embodiment of the presentinvention wherein the position of the valves 12, 16 are combined with the control signals 13 or 17 indicative of synchronous error signals from the comparator or dead center error signals from the adder 42 which are selectively passed through the switch in response to engine speed. For example, a position generator which may be a potentiometer adjustable in response to its respective valve position to apply a signal representative of the position to an adder circuit 49 wherein it is combined with the error signal being passed by the switch 25. In this embodiment, the respective valve l2, 16 is thereby controlled in response to a signal indicative of the error signal in use dependent upon engine speed as modified by a signal indicative of the respective valve position.

Although illustrative embodiments of this invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.

What I claim is: i

a. means for comparing the positions of said first and said second pistons and the angle of rotation of said driveshaft to generate first and second synchronous error signals for said first and said second pistons, respectively;

b. means for comparing the actual dead points of said first and said second pistons and predetermined nominal dead points of each piston to generate first and second dead point error signals;

c. means for relating the first dead point error signal to the second dead point error signal;

d. means responsive to the engine speed for controlling thev amount of fluid in saidfirst and said second hydrostatic motion transducers in accordan ce with said first and said second synchronous error signals when the engine speed is I below a selected speed and with a dead point error signal when said engine speed exceeds a predetermined speed; and

e. means for simultaneously switching the control of both pistons of a cylinder from the synchronous error signal to the dead point error signal and vice versa.

2. The system according to claim 1, wherein said means for relating includes means forcombining said second dead point errorsignal and said first dead point error signal to generate a modified first dead point error signal, and wherein said dead point error signal controlling the amount of fluid in the hydrostatic motion transducers when the engine speed exceeds a predetermined speed, includes said modified first dead point error signal.

3. The system according to claim 2, wherein said dead point error signal controlling the amount of fluid in the hydrostatic motion transducers when the engine speed exceeds a predetermined speed, includes said second dead point error signal.

4. The system of claim 2, wherein said combining means comprises means for subtracting said second dead point error signal from said first dead point error signal to generate said modified first dead point error signal.

5. The system according to claim 2 wherein the means responsive to the engine speed switches over from synchronous regulation to dead point regulation at a higher engine speed than at which it switches over from dead point regulation to synchronous regulation.

6. The system of claim 3 wherein said combining means comprises means for inverting said second dead point error signal, and means for adding an inverted second dead point error signal to said first dead point error signal to generate said modified first dead point error signal.

7. The system of claim 3 wherein said first and said second pistons are vertically aligned as top and bottom driveshaft.

8. The system of claim 3 wherein said dead point error signal generating means comprises for each of said first and said second pistons;

a transformer coil comprising a primary winding, a

pair of firstsecondary windings, and a second secondary winding, Y an alternating current power supply connected to said primary winding,

. a weakly magnetic core operable in response to a respective one of saidfirst and said second pistons approaching a predetermined nominal dead point position to move into said coil a distance representative of the actual point center position of said one of said first and said second pistons, said primary winding and said pair of secondary windings being arranged in a circuit such that the output voltage from said'pair of first secondary windings has a uniformly rising and falling path in at least portions thereof and passes through zero voltage at the predetermined dead center position, and

the second secondary winding being connected such that the voltage induced therein by insertion of the core into the coil uniformly increases and uniformly decreases.

9. The system of claim 8 further comprising; circuit means for measuring the output voltage of saidpair of first'secondary windings when the voltage induced in said second secondary winding reaches a first predetermined threshold level; and for so long as the voltage induced in said second secondary winding remains above a second predetermined threshold level.

10. The system of claim 9 wherein said coil and said core are arranged to generate said first predetermined threshold level when said one of the pistons is at a position closer to said predetermined dead center position than when said second predetermined threshold level is generated.

11. The system of claim 9 wherein said measuring circuit means comprises a peak voltage detector and storage means, and means responsive to said first predetermined threshold value for passing said voltage from said pair of first secondary windings to said peak detector, and in response to said second predetermined threshold value for passing the signal stored in said peak detector to said storage means.

12. The system of claim 8 further comprising means for superimposing a voltage on the output of said pair of first secondary windings of only the coil of said second piston to thereby change the compression value of said cylinder.

13. The systemof claim 8 wherein said combining means comprises means for inverting a function of the voltage of said pair of secondary windings of the second piston, and .means for combining the inverted voltage with the voltage of said pair of secondary windings of said first piston.

14. The system of claim 8 further comprising means for generating a' signal proportional to the' voltage of said pair of first secondary windings, means for integrating said proportional signal, and means for adding said integrated signal and said proportional signal to generate a dead point error signal.

15. The system of claim 14 in which the proportional signal of each piston is equal or proportional to the first secondary voltage of the corresponding piston.

16. The system of claim 14 in which the proportional signal of each pistonis equal or proportional to the first secondary voltage of the corresponding piston, aug mented'by an inverted first secondary voltage or portion thereof of the other piston.

17. The system of claim 14 in which the proportional signal of each piston is equal or proportional to the first secondary voltage of the corresponding piston, augmented by a first secondary voltage or portion thereof of the other piston.

- 18. The system of claim 14 further comprising means for generating a timing signal, comparator means for comparing the time interval between generation of successive dead center point signals for one of the pistons and theoutput of said timing means to thereby obtain a representation of engine. rotational speed, and means responsive to the output of the comparator means for simultaneously switching and selectively controlling the amount of fluid in said first and said second hydro-. static motion transducers in response to said first and said second synchronous error signals, and said modified first deadcenter error signal and said second dead center error-signal.

19. The system of claim 14 wherein said integrating means is responsive to the output of the comparator means indicative of an engine rotational speed for switch over to dead center error signal regulation to begin integration.

20. The system of claim 3 further comprising means for storing said modified first dead point errorsignal,

and said second dead point error signal, and means for retaining the last stored modified first dead point error signal and said second dead point error signal upon power failure of the system.

21. The system of claim 2 further comprising valve' means for controlling the amount of fluid in said first and said second hydrostatic motion transducers, means for generating a signal representative of the position of each of said valves, and means for additively combining said position signals with said dead point error signal.

22. In a method of controlling the relative positions of pistons in an opposed piston engine; wherein said engine includes at least one cylinder, first and second opposed pistons forming a combustion chamber therebetween within said cylinder, a driveshaft, and

means including first and second hydrostatic motion transducers connected to said first and second pistons, respectively, for transmitting piston energy to said drive shaft; the steps comprising;

a. comparing the positions of said first and said second pistons and the angle of rotation of said drive shaft to generate first and second synchronous error signals for said first and said second pistons, respectively;

b. comparing the actual dead point positions of said first and saidsecond pistons and predetermined first and second dead point positions, respectively, to generate first and second dead pointerror signals;

c. relating said dead point error signals to each other;

d. controlling the amount of fluid in said first and said second hydrostatic motion transducers in accordance with said first and said second synchronous error signals when said engine speed is below a predetermined speed, and with a dead 24. The method of claim 22 wherein step (c) comprises subtracting said second dead point error signal from said first dead point error signal to generate a modified first dead point error signal which regulates the amount of fluid in the transducers.

25. The method of claim 22 wherein said first and said second pistons are vertically aligned as top and bottom pistons, respectively, at least substantially above said driveshaft.

26. The method of claim 22, wherein step (c) comprises; inverting said second dead point error signal, and adding the inverted second dead point error signal to said first dead point error signal to produce said dead point error signal. 

1. In a system for controlling the relative positions of pistons in an opposed piston engine; wherein said engine includes at least one cylinder, first and second opposite pistons forming a combustion chamber therebetween within said cylinder, a driveshaft, and means including first and second hydrostatic motion transducers connected to said first and second pistons, respectively, for transmitting piston energy to said driveshaft; the combination comprising; a. means for comparing the positions of said first and said second pistons and the angle of rotation of said driveshaft to generate first and second synchronous error signals for said first and said second pistons, respectively; b. means for comparing the actual dead points of said first and said second pistons and predetermined nominal dead points of each piston to generate first and second dead point error signals; c. means for relating the first dead point error signal to the second dead point error signal; d. means responsive to the engine speed for controlling the amount of fluid in said first and said second hydrostatic motion transducers in accordance with said first and said second synchronous error signals when the engine speed is below a selected speed and with a dead point error signal when said engine speed exceeds a predetermined speed; and e. means for simultaneously switching the control of both pistons of a cylinder from the synchronous error signal to the dead point error signal and vice versa.
 2. The system according to claim 1, wherein said means for relating includes means for combining said second dead point error signal and said first dead point error signal to generate a modified first dead point error signal, and wherein said dead point error signal controlling the amount of fluid in the hydrostatic motion transducers when the engine speed exceeds a predetermined speed, includes said modified first dead point error signal.
 3. The system according to claim 2, wherein said dead point error signal controlling the amount of fluid in the hydrostatic motion transducers when the engine speed exceeds a predetermined speed, includes said second dead point error signal.
 4. The system of claim 2, wherein said combining means comprises means for subtracting said second dead point error signal from said first dead point error signal to generate said modified first dead point error signal.
 5. The system according to claim 2 wherein the means responsive to the engine speed switches over from synchronous regulation to dead point regulation at a higher engine speed than at which it switches over from dead point regulation to synchronous regulation.
 6. The system of claim 3 wherein said combining means comprises means for inverting said second dead point error signal, and means for adding an inverted second dead point error signal to said first dead point error signal to generate said modified first dead point error signal.
 7. The system of claim 3 wherein said first and said second pistons are vertically aligned as top and bottom pistons, respectively, at least substantially above said driveshaft.
 8. The system of claim 3 wherein said dead point error signal generating means comprises for each of said first and said second pistons; a transformer coil comprising a primary winding, a pair of first secondary windings, and a second secondary winding, an alternating current power supply connected to said primary winding, a weakly magnetic core operable in response to a respective one of said first and said second pistons approaching a predetermined nominal dead point position to move into said coil a distance representative of the actual point center position of said one of said first and said second pistons, said primary winding and said pair of secondary windings being arranged in a circuit such that the output voltage from said pair of first secondary windings has a uniformly rising and falling path in at least portions thereof and passes through zero voltage at the predetermined dead center position, and the second secondary winding being connected such that the voltage induced therein by insertion of the core into the coil uniformly increases and uniformly decreases.
 9. The system of claim 8 further comprising; circuit means for measuring the output voltage of said pair of first secondary windings when the voltage induced in said second secondary winding reaches a first predetermined threshold level and for so long as the voltage induced in said second secondary winding remains above a second predetermined threshold level.
 10. The system of claim 9 wherein said coil and said core are arranged to generate said first predetermined threshold level when said one of the pistons is at a position closer to said predetermined dead center position than when said second predetermined threshold level is generated.
 11. The system of claim 9 wherein said measuring circuit means comprises a peak voltage detector and storage means, and means responsive to said first predetermined threshold value for passing said voltage from said pair of first secondary windings to said peak detector, and in response to said second predetermined threshold value for passing the signal stored in said peak detector to said storage means.
 12. The system of claim 8 further comprising means for superimposing a voltage on the output of said pair of first secondary windings of only the coil of said second piston to thereby change the compression value of said cylinder.
 13. The system of claim 8 wherein said combining means comprises means for inverting a function of the voltage of said pair of secondary windings of the second piston, and means for combining the inverted voltage with the voltage of said pair of secondary windings of said first piston.
 14. The system of claim 8 further comprising means for generating a signal proportional to the voltage of said pair of first secondary windings, means for integrating said proportional signal, and means for adding said integrated signal and said proportional signal to generate a dead point error signal.
 15. The system of claim 14 in which the proportional signal of each piston is equal or proportional to the first secondary voltage of the corresponding piston.
 16. The system of claim 14 in which the proportional signal of each piston is equal or proportional to the first secondary voltage of the corresponding piston, augmented by an inverted first secondary voltage or portion thereof of the other piston.
 17. The system of claim 14 in which the proportional signal of each piston is equal or proportional to the first secondary voltage of the corresponding piston, augmented by a first secondary voltage or portion thereof of the other piston.
 18. The system of claim 14 further comprising means for generating a timing signal, comparator means for comparing the time interval betweEn generation of successive dead center point signals for one of the pistons and the output of said timing means to thereby obtain a representation of engine rotational speed, and means responsive to the output of the comparator means for simultaneously switching and selectively controlling the amount of fluid in said first and said second hydrostatic motion transducers in response to said first and said second synchronous error signals, and said modified first dead center error signal and said second dead center error signal.
 19. The system of claim 14 wherein said integrating means is responsive to the output of the comparator means indicative of an engine rotational speed for switch over to dead center error signal regulation to begin integration.
 20. The system of claim 3 further comprising means for storing said modified first dead point error signal and said second dead point error signal, and means for retaining the last stored modified first dead point error signal and said second dead point error signal upon power failure of the system.
 21. The system of claim 2 further comprising valve means for controlling the amount of fluid in said first and said second hydrostatic motion transducers, means for generating a signal representative of the position of each of said valves, and means for additively combining said position signals with said dead point error signal.
 22. In a method of controlling the relative positions of pistons in an opposed piston engine; wherein said engine includes at least one cylinder, first and second opposed pistons forming a combustion chamber therebetween within said cylinder, a driveshaft, and means including first and second hydrostatic motion transducers connected to said first and second pistons, respectively, for transmitting piston energy to said drive shaft; the steps comprising; a. comparing the positions of said first and said second pistons and the angle of rotation of said drive shaft to generate first and second synchronous error signals for said first and said second pistons, respectively; b. comparing the actual dead point positions of said first and said second pistons and predetermined first and second dead point positions, respectively, to generate first and second dead point error signals; c. relating said dead point error signals to each other; d. controlling the amount of fluid in said first and said second hydrostatic motion transducers in accordance with said first and said second synchronous error signals when said engine speed is below a predetermined speed, and with a dead point error signal, when said engine speed exceeds a selected speed; and e. simultaneously switching the control of both of the pistons from the synchronous error signal to the dead point error signal and visa versa.
 23. The method of claim 22 wherein the engine speed at which transfer of control from the synchronous error signal to the dead point error signal occurs is higher than that at which transfer occurs from the dead point error signal to the synchronous error signal.
 24. The method of claim 22 wherein step (c) comprises subtracting said second dead point error signal from said first dead point error signal to generate a modified first dead point error signal which regulates the amount of fluid in the transducers.
 25. The method of claim 22 wherein said first and said second pistons are vertically aligned as top and bottom pistons, respectively, at least substantially above said driveshaft.
 26. The method of claim 22, wherein step (c) comprises; inverting said second dead point error signal, and adding the inverted second dead point error signal to said first dead point error signal to produce said dead point error signal. 